1. Technical Field
The present invention relates to a functional device, a method of manufacturing the functional device, a physical quantity sensor, and an electronic apparatus.
2. Related Art
As a functional device, a physical quantity sensor device is known that includes a fixed electrode arranged to be fixed and a movable electrode spaced apart from and opposed to the fixed electrode and provided to be displaceable and that detects physical quantities such as acceleration and angular velocity on the basis of the capacitance between the fixed electrode and the movable electrode (see, for example, Japanese Patent No. 4238437 (Patent Document 1)).
For example, in the physical quantity sensor device described in Patent Document 1, a single-layer semiconductor substrate or an SOI substrate is used. Each of the fixed electrode and the movable electrode includes plural electrode fingers arranged to form a comb teeth shape. The fixed electrode and the movable electrode are arranged to mesh with each other.
In the physical quantity sensor device described in Patent Document 1, two electrode fingers of the fixed electrode are provided between adjacent two electrode fingers of the movable electrode to face the electrode fingers. The two electrode fingers of the fixed electrode are electrically insulated from each other. Consequently, it is possible to separately measure the capacitance between one electrode finger of the two electrode fingers of the fixed electrode and an electrode finger of the movable electrode opposed to one electrode finger and the capacitance between the other electrode finger of the two electrode fingers of the fixed electrode and an electrode finger of the movable electrode opposed to the other electrode finger and detect physical quantities on the basis of results of the measurement (using so-called differential detection system).
However, in the physical quantity sensor described in Patent Document 1, it is necessary to individually insulate and separate the electrode fingers to prevent the fixed electrode and the movable electrode from becoming conductive to each other. Therefore, manufacturing efficiency is low. In the differential detection system, sensitivity rises when the thickness of the fixed electrode and the movable electrode is large (an aspect ratio is high). However, in the case of Patent Document 1, it is necessary to apply first etching in the thickness direction of the substrate and then apply second etching in the lateral direction of the substrate. To increase the thickness of the fixed electrode and the movable electrode, it is necessary to form the substrate thick in advance. Therefore, it is difficult to increase the thickness of the electrodes from the viewpoint of manufacturing efficiency. In general, the SOI substrate is expensive and manufacturing cost increases.